Tony's hubris was his ego and contradictory nature, on one hand he preaches "Honor and loyalty" then in the same breath he'll say "Fuck all that honor and loyalty shit"....

"Seven deadly sins Ton', and yours is...Pride" - Silvio to Tony in "With All Due Respect"....

Mistakes by Tony:
- Not allowing Richie to earn or giving him the proper respect once he came home.
- Making Chrissy
- Constantly pissing of NY with his ego, especially over the HUD and Zellman
- Hitting Ralph...later on killing Ralph which cost him millions potentially.
- Letting Chris be an acting Capo while Paulie was in the can and chaos ensured
- Getting involved with internal power struggles in the Lupertazzi family and contracting hitters from Italy to solve them. (Which if found out would erase the Sopranos from history)
- Giving Tony B. a pass and mercy kill rather than let NY get their proper revenge which would sow the seeds for the war with NY
- Not allowing Eugene to retire (which caused more crew problems)
- Not protecting Vito from Phil
- Smashing Cocoa's teeth
- Continuing to gamble big and heavy with the loss of his big earners.